Control devices for driers



April 5, 1966 T. R. SMITH 3,243,891

CONTROL DEVICES FOR DRIERS Filed April 2'7, 1962 (FAse/c' United StatesPatent 3,243,891 CONTROL DEVICES FOR DRIERS Thomas R. Smith, Newton,Iowa, assignor to The Maytag Company, Newton, Iowa, a corporation ofDelaware Filed Apr. 27, 1962, Ser. No. 190,675 4 Claims. (Cl. 34-45)This is a continuation-in-part of applications of Thomas R. Smith, Ser.No. 40,663, filed July 5, 1960, now forfeited, and Ser. No. 22,323,filed Apr. 14, 1960, now abandoned.

This invention relates to devices for directly determining the conditionof fabrics employed in a control system of a machine for drying fabrics,and more particularly, to electrodes for contacting and completing anelectrical circuit through fabrics.

Many attempts have been made to control the termination point of dryingoperations as related, directly, or indirectly, to the condition of thefabrics. Elberty Patent No. 2,045,381, for example, relies upon thechange in conductivity of the fabrics as the moisture is removed inorder to discontinue operation of a drying machine at the momentelectrical conductivity of the fabrics, as sensed directly betweenconductors in the drum, attains a predetermined value.

In other control systems, the humidity of the air within the drier ismeasured to determine when the drying operation should be terminated,instead of direct measurements of the electrical conductivity of thefabrics, illustrated in Horecky Patent No. 2,820,304, for example.Humidity determinations are an unreliable index of the condition of thefabrics, and control. systems dependent thereon contain an inherentdeficiency.

. In still other systems attempts have been made to control thetermination of the drying period by thermostats in the drier. In thesesystems the thermostats operate to shut-off the heaters when thetemperature within the drying cabinet rises above a set value whichoccurs when most of the clothes have been dried. Again, the control doesnot insure that all of the fabrics have been dried.

It is an object of the present invention to provide a control system fora clothes drier responsive to the dry condition of the fabrics beingtreated. It is a further object of the invention to provide a system forcontrolling termination of a drying operation that is responsive to thedirect determination of the electrical conductivity of the fabrics, soas to obtain reliable shut-off of the drying operation. It is a stillfurther object of the invention to provide a system whereby directresponse of the control to the dryness or conductivity of fabrics ismade practical or feasible for home laundry clothes driers. Furtherobjects and advantages of this invention will become evident as thedescription proceeds and from an examination of the accompanyingdrawings which illustrate several embodiments of the invention and inwhich similar numerals refer to similar parts throughout the severalviews.

In the drawings:

FIGURE 1 is a view in vertical section, partly broken away showing adrier which incorporates the control system of the invention;

FIGURE 2 is an enlarged view in longitudinal section of one of thebafiies in the drum, illustrating the arrangement of electrodes thereon;

FIGURE 3 is a sectional view of one form of electrode of the invention;and

FIGURE 4 is a sectional view of a modified form of electrode.

Briefly described, the invention relates to a control systemin whichconductors, electrodes, or probes, directly "ice contact fabrics beingdried to directly determine their electrical conductivity. Theconductors, electrodes, or probes, which are mounted in a revolubledrum, are made or coated with a material that is a good electricalconductor when wet or moist, but a poor electrical conductor when dry.

Referring now to the drawings, FIGURE 1 shows a clothes drier having abase frame 10 which serves as a support for upstanding channel b-asemembers 11 and 12 which together with cross piece 14 support the hollowblower housing casting 17. Housing 17 includes a tubular portion 21, adivider wall 20 having a rearwardly flared inner portion defining anintake into an impeller chamber, and radially directed longitudinal webs22 which converge toward each other to provide a retainer member 23. Apassageway 26 is located between the tubular portion 21 and the bearingretainer member 23 which transverses the supporting webs Within member23 is journalled a revoluble drum drive shaft 31 which projects fromboth ends of the housing 17. Affixed to drum drive shaft 31 at the rearof the cabinet is a large pulley 33 which is driven by motor 34 throughmotor pulley 36, main drive belt 37, a speed reduction system (notshown) and belt 40.

The opposite or forward end of the drum drive shaft 31 is rigidlyconnected to the drum spider member 46 which has radiating spokes 51that support rim 52. A heat resistant sealing member 54 encircles thefront periphery of blower housing 17 and the circular shoulder 55located on the rear portion of drum spider 46.

A horizontally mounted tumbling drum has a rear wall 61 which is securedto rim 52 for support and rotation by shaft 31. Rear drum wall 61 isimperforate except for a central exhaust opening 62.

The periphery of rear wall 61 is flanged to form a supporting shoulderfor the imperforate cylindrical side wall 65 which carries the clotheselevating vanes 66 for tumbling clothing within drum 60 during rotationof the latter member. Cylindrical side wall 65 is connected to the frontdrum wall 67.

Front wall 67 has a centrally located access opening 68 and a circularperforate portion 69 located concentrically to access opening 68. Thisperforate portion 69', formed by several concentric rows of holes,serves as the air intake into drum 60.

The cabinet 70 which is fastened to base frame 10 and which encloses theentire drying mechanism has an access opening 71 aligned to drum accessopening 68 thereby allowing both of openings 68 and 71 to receive thedoor gasket 72. The door 73 is hinged to form with gasket 72 an airtightseal for cabinet 70.

Fastened to cabinet 70 is the shroud or cowling member 74. Locatedbetween shroud 74 and the front drum wall 67 is an open coil electricheating element 75 which extends completely around the inside of cowlingmember 74 to raise the temperature of air passing through perforateportion 69 in the front drum wall 67. It will be understood that a gasheater may be used in place of the electrical element.

Air flow into drum 60 through the perforate area 69 and into the blowerhousing 17 is produced by rotation of the revoluble impeller member 76located in blower housing 17. Fan pulley 77 is connected to the drivingmotor 34 by main drive belt 37. The blower housing casting 17 supports acycling thermostat 7 8 which is connected in series with the heatingelement 75 in order to maintain the interior of drum 60 at the properselected drying temperature.

In order to measure the electrical conductivity or resistance fordetermining the condition of dryness of the 3 fabrics, electrodes orprobes 80, 81 are mounted within the drum 60. In the form shown, a pairof electrodes of opposite polarity are spirally wound about each of thedrum bafiles 66 to provide a maximum amount of contacting or probingsurfaces exposed to the fabrics placed within the drum. As bestillustrated in FIGURE 2, the electrodes are preferably set in recessesor grooves in the bafll'es containing therebetween outwardly projectingshoulders, or ridges, 95'to' prevent shorting therebetween by metallicobjects sometimes attached tothe fabrics, for example, metal buttons,clips, buckles, and the like.

In order to reduce further the response of the electrodes to metallicobjects, the electrodes 80, 81 are formed with materials that are goodelectrical conductors when wet, or moist, and relatively poor electricalconductors when dry. This may be accomplished by ordinary fabric coatingas shown in FIGURE 3. As shown, the electrode 80' has an outer layer offabric 101. The fabric is more electrically conductive when wet thandry. Other suitable coatings may include layers of chemicals having thesame characteristics.

Alternatively the electrodes 80, 8 ay be formed of metals possingsimilarproperties, for mple, aluminum wire with an anodic coating, as sh'own'inFIGURE 4. As shown, the electrode 80" is formed of aluminum, the outersurface of'whi'ch is anodized at 102. Special preference is given toanodized aluminum wire since it additionally resists wear and if it ischipped or worn tend'sto be self repairing in the environment of adrier.

Electrical energy is supplied to electrode 80 by lead 84 that isconnected to brush 85 which engages the stationary slip ring 86 whilethe drum 60 is rotating. The slip ring" 86 may be supported on anelectrically insulative band 87 mounted on housing 17; Slip ring 86 isin turn connected to a lead 90 which runs to the control unit 92.Electrode 81 may also be supplied with electrical energy of the oppositepolarity to electrode 80 by similar arrangement of brushes and sliprings. It is preferred, however, to ground electrode 81 to the rotatabledrum 60', so that it is supplied by current from lead 91 which is alsogrounded to the framework of the drier.

The automatic control unit 92 may be secured to the upper portion of thecabinet. Leads 90, 91 enter the control unit and are connected to thecontrol circuit to be described hereinafter.

Bafiles 66 are formed of electrically non-conductive material in orderto insulate the electrodes. However, the electrodes are electricallyshorted by contacting the wet fabrics during tumbling. Ordinarily, aplurality of baffles 66 are mounted within the drum 60, each of which isprovided with electrodes 80, 81, and the respective electrodes of'allthe battles connected in parallel although a single baflie provided withelectrodes may be used. Referring now to FIGURE 2, which illustrates thebaffles in detail, the wire electrodes 80, 81 are spirally wound on thesurface of the baflles; the ends 96, 9'7 being secured to the bottominterior of the baffles by suitable insulators. The leads 83, 84 fromthe electrodes are elect'r'ically connected to the control system andare preferably insulated. To further insure minimum current leakage fromelectrodes 80, 81,. insulation may be advantageously provided on theentire electrode except in the area of fabric contact, namely, the crownarea 93 of the baflles. In the crown area 93, the electrodes are bare topermit electrical shorting by Wet fabrics during tumbling.

The bafiles may be formed of synthetic resinous materials so as to beelectrically insulative, and may be hollow. The shoulders, or ridges 95are molded into the surface. Screw sockets 99 are formed in the base ofthe bafiles for mounting to the interior surface of the drum.

Since the electrodes contact the fabrics for determining fab c e e t ial conducti ity, sh ing f t e e e trodes by metallic objects is, ofcourse, undesirable. By positioning shoulders, or ridges 95, however,between ad acent electrodes of a height greater than the outer diameterof the electrodes, simultaneous contact by flat'metallic objects ofadjacent electrodes is avoided. Thus, fabrics because of their limp,flexible nature, drape over the shoulders, or ridges to complete anelectrical circuit through the electrodes. On the other hand, metallicobjects because of their inherent rigidity, are prevented fromcontacting adjacent electrode pairs by the shoulders, or ridges 95. Theresult is selective determination of fabric electrical resistance.

In addition, because the electrodes are formed of ma terials that aregood electrical conductors when wet and poorer electricalconductors whendry, as explained 'hereinabove, response of the automatic control unitto the electrical properties of metallic objects in the load arereduced.-

In the drawings and specification there have been set forth severalembodiments of the invention, and although specific terms are employed,these are used in a generic and descriptive sense only, and not forpurposes of limitation. Changes in form and the proportion. of parts, aswell as the substitution of equivalents are contemplated, ascircumstances may suggest or render expedient, without departing fromthe spirit or scope of this invention as further defined in thefollowing claims.

I claim:

1. In a drier having an electrical control system for termination of thedrying operation, a revoluble drum for tumbling the fabrics, means forrotating said druirr to tumble the fabrics, heating means for dryingfabrics in said drum, and at least one pair of spacedelectrodespositioned within said revoluble drum for contacting the"fabrics as they are tumbled, said electrodes including meis tu'reabsorptive material on the surface of at least one of said electrodepair with the absorptive material on said' one electrode being spacedand insulatedfrom the second of said electrode pair, said absorptivematerial being a good electrical conductor having conductancecharacteristics above a first value when moist for selectively ef-'fecting completion of a circuit through the fabrics con" tacting saidpair of electrodes when said fabrics are wet? and preventing completionof a circuit through said ah sorptive material in the absence of contactby said wet" fabrics, and further being a relatively poor electricalconductor having conductance characteristics below said first value whendry for preventing completion of a circuit through metallic objects whensaid fabrics are dry.

2. In an apparatus for drying fabrics having a control system forterminating the drying operation a revoluble drum for drying fabrics,means for rotating said drum to tumble the fabrics, heating means fordrying fabrics in said drum, at least one bafile member mounted on theinterior surface of said drum for engaging the fabrics, at least onepair of spaced electrodes positioned onsaicl baifie member, saidelectrodes including moisture absor tive material on the surface of atleast one of said electrode pair, said absorptive material being a goodelectrical conductor having conductance characteristics above a firstvalue when moist and relatively poor electrical conductor havingconductance characteristics below said first value when dry, andinsulation means covering a first portion of at least said oneelectrode, and absorptive material said one electrode having a secondportion exposed for contact by the fabrics to selectively limitcompletion of a circuit between said pair of electrodes to an electricafpath through the wet fabrics.

3. In a drier having a control system for terminating; the dryingoperation, a revoluble drum for drying fabrics; means for rotating saiddrum to tumble the fabrics, heat-. ing means for drying fabrics in saiddrum, baffle members; mounted on the interior surface ofsaid drum forengag-. i s he fab i t l ast one of said bafile membersformed ofelectrically insulative materials, and at least one pair of spacedelectrodes positioned on said baffle member, said electrodes includingmoisture absorptive material that has relatively higher electricalconductivity when moist than when dry on the surface of at least one ofsaid electrode pair, the absorptive material on said one electrode beingspaced and insulated from the second of said electrode pair ofselectively effecting completion of a circuit through the wet fabricscontacting said pair of electrodes and preventing completion of acircuit through said absorptive material in the absence of contact bysaid wet fabrics.

4. In an apparatus for drying fabrics, having a control system forterminating the drying operation, a revoluble drum for drying saidfabrics, means for rotating said drum to tumble the fabrics, heatingmeans for drying said fabrics in said drum, and at least one pair ofspaced electrodes positioned within said drum and electrically exposedfor contacting the fabrics as tumbled, said exposed electrodes includingmoisture absorptive material that has relatively higher electricalconductivity when moist than when dry on the surface of at least one ofsaid electrode pair, the absorptive material on said one electrode beingspaced and insulated from the second of said electrode pair.

References Cited by the Examiner UNITED STATES PATENTS 1,526,127 2/1925Flick 204-58 2,045,381 6/1936 Elberty 34-55 2,234,858 3/1941 Brown338-35 2,237,006 4/1941 Koller 338-35 2,364,996 12/ 1944 Osterheld338-245 2,381,299 8/1945 McCulloch 338 2,617,972 11/1952 Nutter 338352,714,149 7/1955 Craig 33835 2,793,526 5/1957 Dalglish 33835 2,820,3041/1958 Horecky 34-45 2,991,641 7/1961 Woodling 34-45 X FOREIGN PATENTS877,553 9/1961 Great Britain.

OTHER REFERENCES Publication: Electronics (Maytag Electronic Dryers), 10pages, 1960.

ALDEN D. STEWART, Primary Examiner.

NORMAN YUDKOFF, PERCY L. PATRICK,

Examiners. JOHN J. CAMBY, Assistant Examiner.

1. IN A DRIER HAVING AN ELECTRICAL CONTROL SYSTEM FOR TERMINATION OF THEDRYING OPERATION, A REVOLUBLE DRUM FOR TUMBLING THE FABRICS, MEANS FORROTATING SAID DRUM TO TUMBLE THE FABRICS, HEATING MEANS FOR DRYINGFABRICS IN SAID DRUM, AND AT LEAST ONE PAIR OF SPACED ELECTRODESPOSITIONED WITHIN SAID REVOLUBLE DRUM FOR CONTACTING THE FABRICS AS THEYARE TUMBLED, SAID ELECTRODES INCLUDING MOISTURE ABSORPTIVE MATERIAL ONTHE SURFCE OF AT LEAST ONE OF SAID ELECTRODE PAIR WITH THE ABSORPTIVEMATERIAL ON SAID ONE ELECTRODE BEING SPACED AND INSULATED FROM THESECOND OF SAID ELECTRODE PAIR, SAID ABSORPTIVE MATERIAL BEING A GOODELECTRICAL CONDUCTOR HAVING CONDUCTANCE CHARACTER-